SeaSpace TeraScan 1.5M Operation And Maintenance Manual page 204

If the second port (nav-2) is used, the following variables must also be defined:
[nav-2] nav.type
[nav-2] nav.device
[nav-2] nav.msgfmt
In general, it is best to run the port at the fastest NMEA baud rate possible.
Configuration Example (in system.config):
port [nav-1] is for NMEA data, sent at 4800 baud, serial port is /dev/term/1
[nav-1]
nav.type: nmea
nav.device: /dev/term/1
nav.baudrate: 4800
Example:
Read the NMEA messages forever:
[1]% nmea_monitor >/dev/console &
Files:
$PASSDIR/SHMEM_NMEA
The file $PASSDIR/SHMEM_NMEA must be defined so that shared memory can be allocated to store
the NMEA data. It is a zero-length file with read/write permissions.
188 SeaSpace Corporation
use by the system until another ship heading is received. Recommended value
is 4. If nav.timeout is non-zero and ship heading is not received, the pass will
not be tracked and the "no ship heading" error will be logged.
Note: If nav.timeout setting is >0, there may be no heading sent by the NMEA
equipment when the ship is in port. To receive data when in port, the
nav.timeout value must be set to zero and zaptsched must be run to restart
nmea_monitor, then the command shipheading can be run to set the bearing
while at the dock. When the ship returns to sea, the nav.timeout value must
be reset to non-zero again to provide BAD values when the NMEA equipment
fails.
type of device associated with the second port.
device name of the serial port attached to the second NMEA port.
Example: "/dev/term/3".
(same values as the first port)
Message format for data sent to nmea_monitor
0183 v2.10/1=NMEA 0183 Version 2.10
0183 v2.30=NMEA 0183 Version 2.30
0183 v3.00=NMEA 0183 Version 3.00
nav1-cdg/2=NAV1 -CDG